The proposed research is a combined genetic and biochemical study of mitochondrial biogenesis in Neurospora with the long range goals of defining the roles of the nuclear and metochondrial genetic systems and understanding how these roles are coordinated and modulated. Specific aims focus on: (a) mitochondrial ribosome assembly, a process which requires interaction between the nuclear and mitochondrial genetic systems, and (b) the function and genetic mapping of Neurospora mtDNA. A number of goals are related to the characterization of the mitochondrially-synthesized ribosomal protein, S-5. Other goals are related ot intramitochondrial plasmid DNAs recently discovered in our laboratory. We will continue to characterize these plasmids to determine their function. We will also determine whether the plasmids can be used as vehicles to introduce genes into mitochondria by transformation.